The present invention relates to on-board real-time diagnostics of mobile technical systems.
In order to detect faults or monitor ageing processes in vehicle systems, the normal procedure involves bringing the system into a mechanical workshop where the behavior can be tested using predefined and controlled conditions. Design tolerances and references can then be compared with measured variables to provide an accurate estimate concerning not only individual items but also the overall functioning and degradation of the system.
An internal combustion engine can be characterized by an engine speed/torque curve. A corresponding analysis tool for a fuel cell powertrain is a polarization curve as shown in FIG. 2. This polarization curve shows the effect of discharging current from a fuel cell system on the cell voltage and power. The curve is usually derived from a specifically designed dynamometer test cycle where the current and voltage are recorded at predefined static load points. The polarization curve, such as shown FIG. 2, results from an interpolation of those static load points.
The present invention results from a recognition that accomplishing of this diagnostics on an on-board component in real-time during normal driving would be a valuable tool not only for customers and field technicians, but also for development engineers. The ability to have a real-time diagnostics would lead to lower maintenance cost, faster problem resolution and shorter design cycles. It has also been recognized that the task of such on-line diagnostics is very complex with a principle obstacle being the range of varying dynamic influences. For example, with fuel cell stacks, the operational temperature, air/hydrogen gas temperatures and pressures inside the stack and the recordings of the fuel cell voltage and current lead to a range of uncertainty of the measurement points instead of more defined points recorded at predefined static loads. This comparison can be seen in FIG. 3 which compares work bench test data with data during normal driving.
This range of uncertainty in the factors can be attributed to both the external environment as well as control strategies of different system components. The system is rarely in equilibrium. As an example, the polarization of a fuel cell depends not only on the current load request, but also on the pressure on the air and hydrogen side. Furthermore the system behaves quite differently at the same point in the load diagram during positive and negative load changes.
As a result, the task of on-board diagnostics is significantly more complex than the stationary diagnostics because of a series of confounding variables.
It is an object of the present invention to provide on-board diagnostics of such a system in real-time during normal driving which leads to lower maintenance costs, quicker response time for problem resolution and shorter design cycles.
According to the present invention, known adaptive techniques are applied to estimate static characteristic curves such as those observed in a workshop test facility based on observed, non-stationary everyday driving data. As a result, the aforementioned confounding variables are eliminated with a resulting estimated characteristic curve which can be compared to a reference curve.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.